text: Exploitation of tritrophic interactions can benefit agricultural systems. Biocontrol of crop pests can be exerted by the third trophic level, given an adequate population of natural enemies. However, the widespread use of pesticides or Bt crops can undermine natural enemies’ success. In some cases, populations of predators and parasitoids are decimated, necessitating even greater use of insecticide because the ecological service they provided in controlling herbivores has been lost.
  Even when pesticides are not widely used, monocultures often have difficulty support natural enemies in great enough numbers for them to diminish pest populations. A lack of diversity in the first trophic level is linked to low abundance in the third because alternative resources that are necessary for stable, large natural enemy populations are missing from the system. Natural enemy diets can be subsidized by increasing landscape diversity through companion planting, border crops, cover crops, intercropping, or tolerance of some weed growth. When nectar or other sugar-rich resources are provided, the natural enemy population thrives.